1. Field of the Invention
This invention relates to a film for a multiple bag composed of at least two sheets of film which are not laminated to one another and can freely be mutually slipped, said film for a multiple bag being used for automatically making a bag and packing the bag with a liquid, a semifluid, a powder or the like for business use, the multiple bag obtained therefrom being excellent in mechanical characteristics such as pinhole resistance, drop impact strength and the like and the said film for a multiple bag being much superior in workability in an automatic bag-making-and-packing machine.
2. Description of the Related Art
Materials such as liquid, semifluid, powder and the like for business use have heretofore been packed in a metal container and then put to distribution including transportation, custody, sale and the like. However, metal containers are disadvantageous in that they are bulky even after use, the contents of the containers are difficult to take out, the treatment of the containers after use is difficult, etc.
A packaging method called "in-box" by which the above contents are packed in a plastic-made bag and the thus packed bag is placed in a corrugated box and distributed is now being widely put to practical use.
In the case of packed bags for the in-box, it is preferable to effect the packing by an automatic bag-making-and-packing machine in view of the efficiency of the contents-packing. On the other hand, the packed bag contains a large weight of contents and has a large size, and hence, is required to have a high mechanical strength. Also, the contents are often fluids, semifluids or powders which are easily escaped from a small rent of the container and are, once escaped, difficult to treat, and the packed bag is required to have mechanical strength characteristics such as drop impact resistance, pinhole resistance, cold resistance and the like.
In order to increase the strength of the packed bag, there is well-known a method in which high-strength films of nylon, polyester or the like are laminated through a fusible layer. For further enhancing the strength, it is possible to laminate other various films or increase the thickness of the high-strength film; however, the extreme increase of the thickness of the film hardens the film, and as a result, the flexure stress applied to the film is increased, the flexural fatigue, pinhole resistance and drop impact resistance are deteriorated, and the packing workability is lowered. Therefore, at present, the above problem cannot be solved by only increasing the thickness of the film.
Under such circumstances, there has been proposed a multiple bag in which the films constituting the bag are not laminated and are in the mutually movable state. In the case of this multiple bag, even when a pinhole is formed in one sheet of film, the other sheets of film are flaw-free, and even when one independent sheet of film receives the flexure stress another sheet of film can be slipped to be escaped from the flexure stress, so that there is no fear that an extreme large flexure stress may be applied. Therefore, the bag has excellent mechanical strength characteristics and is excellent as a bag for the bag-in-box.
However, when diverse films are merely put on one another and rolled in an automatic bag-making-and-packing machine, the films cause position deviation and winding breakage, and hence, this method has been by no means put to practical use.
Accordingly, a multiple film in which films are merely put on one another cannot be used in an automatic bag-making-and-packing machine, and hence, the multiple bag actually used is employed in a system in which bag-making and packing are separately carried out, that is, a system in which a previously prepared multiple bag with a tap is packed with the contents introduced through the tap. This system is inferior in working efficiency and it is unavoidable for air to remain in the sealed bag. Hence, there is such a fear that the remaining air may accelerate the deterioration of the contents.
On the other hand, there is proposed a method in which diverse films are previously continuously fused at their both-side edge portions to one another and then fed to an automatic bag-making-and-packing machine. However, even in this method, the diameter of a roll formed by winding the inside film and the diameter of a roll formed by winding the outside film are delicately different, and hence, when the films are wound repeatedly, said delicate difference in diameter results in a wrinkle and a sag and when the films wound up become disordered, so that only a small roll of film can be provided, and owing to a frequent roll-exchange, at present, the workability as a whole is not enhanced.
In addition, this method comprises a step of fusing both-side edge portions of the films and this step requires a given heating time and hence requires a long period of time as a whole for the processing. Therefore, the method is not practical.
Thus, there have been required films from which a multiple bag can be easily produced using an automatic bag-making-and-packing machine.